Coil constructions for improved inductive energy transfer

TECHNICAL FIELD

0001The present invention relates generally to inductive energy transfer, and more particularly to coil constructions for improved inductive energy transfer in an inductive energy transfer system.

BACKGROUND

0002Many electronic devices include one or more rechargeable batteries that require external power to recharge from time to time. Often, these devices may be charged using a similar power cord or connector, for example a universal serial bus (“USB”) connector. However, despite having common connection types, devices often require separate power supplies with different power outputs. These multiple power supplies can be burdensome to use, store, and transport from place to place. As a result, the benefits of device portability may be substantially limited.

0003Furthermore, charging cords may be unsafe to use in certain circumstances. For example, a driver of a vehicle may become distracted attempting to plug an electronic device into a vehicle charger. In another example, a charging cord may present a tripping hazard if left unattended.

0004To account for these and other shortcomings of portable electronic devices, some devices include an inductive charging device. The user may simply place the electronic device on an inductive charging surface of a charging device in order to transfer energy from the charging device to the electronic device. The charging device transfers energy to the electronic device through inductively coupling between a transmitter coil in the charging device and a receiver coil in the electronic device. Under some circumstances, however, losses in the transmitter and receiver coils reduce the efficiency of the energy transfer. As one example, losses can be produced by the resistance of the wire or wires in the coils.

SUMMARY

0005Embodiments described herein provide wire and coil constructions that can reduce losses in the transmitter and receiver coils. In one aspect, an inductor coil in a portable electronic device includes three or more layers of a single wire. The windings of the coil are interlaced within at least two of the three or more layers such that both an input end and an output end of the wire enter and exit the coil on a same side of the coil. The portable electronic device may be a transmitter device or a receiver device. The input end and the output end of the wire can abut one another at the location where the input and output ends enter and exit the coil. A shape of at least one edge of the inductor coil may complement a surface of the electronic device.

0006In another aspect, the wire in the inductor coil can be constructed with two or more bundles of strands that are twisted around an axis that extends along the length of the wire. Each bundle can include multiple individual conductive strands that may also be twisted around the axis that extends along the length of the wire. As one example, a bundle can include seven individual conductive strands that are twisted around the axis that extends along the length of the wire. The wire may include four bundles are twisted around the axis.

0007In yet another aspect, a method for forming an inductor coil can include forming the inductor coil on a mandrel by winding the wire on or around the mandrel. The inductor coil is formed into a first inductor coil structure. Typically, a bonding agent or adhesive is disposed on the windings to fix or secure the inductor coil structure. The bonding agent may then be treated to cause the bonding agent to become malleable. In some embodiments, the bonding agent can be heated to produce a pliable bonding agent. The inductor coil is then formed into a second inductor coil structure by forming the inductor coil onto a mold or surface. For example, an inductor coil can be constructed in a rectangular shape. The bonding agent in the coil can be heated and the inductor coil pressed on a curved surface to produce a trapezoid shape. At least one edge or surface of the coil, the edge in contact with the curved surface, will be formed into a shape that complements the curved surface.

BRIEF DESCRIPTION OF THE DRAWINGS

0008Embodiments of the invention are better understood with reference to the following drawings. The elements of the drawings are not necessarily to scale relative to each other. Identical reference numerals have been used, where possible, to designate identical features that are common to the figures.

0009<figref idref="DRAWINGS">FIGS. 1 and 2</figref> are perspective views of one example of an inductive energy transfer system;

0010<figref idref="DRAWINGS">FIG. 3</figref> depicts a cross-sectional view of the inductive energy transfer system taken along line <b>3</b>-<b>3</b> in <figref idref="DRAWINGS">FIG. 2</figref>;

0011<figref idref="DRAWINGS">FIG. 4</figref> depicts a simplified block diagram of one example of the inductive charging system <b>100</b> shown in <figref idref="DRAWINGS">FIGS. 1 and 2</figref>;

0012<figref idref="DRAWINGS">FIG. 5</figref> is a perspective view of a bundle suitable for use in the transmitter coil <b>406</b> and/or the receiver coil <b>408</b> shown in <figref idref="DRAWINGS">FIG. 4</figref>;

0013<figref idref="DRAWINGS">FIG. 6</figref> is cross-sectional view of the bundle <b>506</b> taken along line <b>6</b>-<b>6</b> in <figref idref="DRAWINGS">FIG. 5</figref>;

0014<figref idref="DRAWINGS">FIG. 7</figref> is cross-sectional view of the bundle <b>506</b> taken along line <b>7</b>-<b>7</b> in <figref idref="DRAWINGS">FIG. 5</figref>;

0015<figref idref="DRAWINGS">FIG. 8</figref> is cross-sectional view of the bundle <b>506</b> taken along line <b>8</b>-<b>8</b> in <figref idref="DRAWINGS">FIG. 5</figref>;

0016<figref idref="DRAWINGS">FIG. 9</figref> is a perspective view of one example of a wire suitable for use in the transmitter coil <b>406</b> and/or the receiver coil <b>408</b> shown in <figref idref="DRAWINGS">FIG. 4</figref>;

0017<figref idref="DRAWINGS">FIG. 10</figref> is a cross-sectional view of the wire <b>900</b> taken along line <b>10</b>-<b>10</b> in <figref idref="DRAWINGS">FIG. 9</figref>;

0018<figref idref="DRAWINGS">FIG. 11</figref> is a perspective view of one example of a coil suitable for use as the transmitter coil <b>406</b> and/or the receiver coil <b>408</b> shown in <figref idref="DRAWINGS">FIG. 4</figref>;

0019<figref idref="DRAWINGS">FIG. 12</figref> is a cross-sectional view of the coil <b>1100</b> taken along line <b>12</b>-<b>12</b> in <figref idref="DRAWINGS">FIG. 11</figref>;

0020<figref idref="DRAWINGS">FIG. 13</figref> is an expanded view of the transmitter device <b>102</b> shown in <figref idref="DRAWINGS">FIGS. 1 and 2</figref>;

0021<figref idref="DRAWINGS">FIGS. 14 and 15</figref> are expanded views of other examples of a transmitter device; and

0022<figref idref="DRAWINGS">FIG. 16</figref> is a flowchart of a method for forming the inductor coil shown in <figref idref="DRAWINGS">FIGS. 13-15</figref>.

DETAILED DESCRIPTION

0023Embodiments described herein provide an inductive energy transfer system that transfers energy inductively from a transmitter device to a receiver device to charge a battery or to operate the receiver device. Additionally or alternatively, communication or control signals can be transmitted inductively between the transmitter and receiver devices. For example, while charging, high frequency pulses can be added on top of the inductive charging frequency to enable both charging and communication. Alternatively, the transferred energy can be used solely for communication. Thus, the terms “energy”, “power”, or “signal(s)” are meant to encompass transferring energy for wireless charging, transferring energy as communication and/or control signals, or both wireless charging and the transmission of communication and/or control signals.

0024Referring now to <figref idref="DRAWINGS">FIG. 1</figref>, there is shown a perspective view of one example of an inductive energy transfer system in an unmated configuration. The illustrated embodiment shows a transmitter device <b>102</b> that is configured to wirelessly pass energy to a receiver device <b>104</b>. The receiver device <b>104</b> can be any electronic device that includes one or more inductors, such as a portable electronic device or wearable accessory.

0025The wearable accessory, such as depicted in <figref idref="DRAWINGS">FIG. 1</figref>, may be configured to provide health-related information or data such as but not limited heart rate data, blood pressure data, temperature data, oxygen level data, diet/nutrition information, medical reminders, health-related tips or information, or other health-related data. The associated monitoring device may be, for example, a tablet computing device, phone, personal digital assistant, computer, and so on.

0026A wearable accessory may include a coupling mechanism to connect a strap or band useful for securing to a user. For example, a smart watch may include a band or strap to secure to a user's wrist. In another example, a wearable health assistant may include a strap to connect around a user's chest, or alternately, a wearable health assistant may be adapted for use with a lanyard or necklace. In still further examples, a wearable device may secure to or within another part of a user's body. In these and other embodiments, the strap, band, lanyard, or other securing mechanism may include one or more electronic components or sensors in wireless or wired communication with the accessory. For example, the band secured to a smart watch may include one or more sensors, an auxiliary battery, a camera, or any other suitable electronic component.

0027In many examples, a wearable accessory, such as depicted in <figref idref="DRAWINGS">FIG. 1</figref>, may include a processor coupled with or in communication with a memory, one or more communication interfaces, output devices such as displays and speakers, one or more sensors, such as biometric and imaging sensors, and one or more input devices such as buttons, dials, microphones, or touch-based interfaces. The communication interface(s) can provide electronic communications between the communications device and any external communication network, device or platform, such as but not limited to wireless interfaces, Bluetooth interfaces, Near Field Communication interfaces, infrared interfaces, USB interfaces, Wi-Fi interfaces, TCP/IP interfaces, network communications interfaces, or any conventional communication interfaces. The wearable device may provide information regarding time, health, statuses or externally connected or communicating devices and/or software executing on such devices, messages, video, operating commands, and so forth (and may receive any of the foregoing from an external device), in addition to communications.

0028Although the system <b>100</b> illustrated in <figref idref="DRAWINGS">FIGS. 1 and 2</figref> depicts a wristwatch or smart watch, any electronic device may be suitable to receive energy inductively from a transmitter device. For example, a suitable electronic device may be any portable or semi-portable electronic device that may receive energy inductively (“receiver device”), and a suitable dock device may be any portable or semi-portable docking station or charging device that may transmit energy inductively (“transmitter device”).

0029The transmitter device <b>102</b> and the receiver device <b>104</b> may each respectively include a housing <b>106</b>, <b>108</b> to enclose electronic, mechanical and structural components therein. In many examples, and as depicted, the receiver device <b>104</b> may have a larger lateral cross section than that of the transmitter device <b>102</b>, although such a configuration is not required. In other examples, the transmitter device <b>102</b> may have a larger lateral cross section than that of the receiver device <b>104</b>. In still further examples, the cross sections may be substantially the same. And in other embodiments, the transmitter device can be adapted to be inserted into a charging port in the receiver device.

0030In the illustrated embodiment, the transmitter device <b>102</b> may be connected to a power source by cord or connector <b>110</b>. For example, the transmitter device <b>102</b> can receive power from a wall outlet, or from another electronic device through a connector, such as a USB connector. Additionally or alternatively, the transmitter device <b>102</b> may be battery operated. Similarly, although the illustrated embodiment is shown with the connector <b>110</b> coupled to the housing of the transmitter device <b>102</b>, the connector <b>110</b> may be connected by any suitable means. For example, the connector <b>110</b> may be removable and may include a connector that is sized to fit within an aperture or receptacle opened within the housing <b>106</b> of the transmitter device <b>102</b>.

0031The receiver device <b>104</b> may include a first interface surface <b>112</b> that may interface with, align or otherwise contact a second interface surface <b>114</b> of the transmitter device <b>102</b>. In this manner, the receiver device <b>104</b> and the transmitter device <b>102</b> may be positionable with respect to each other. In certain embodiments, the second interface surface <b>114</b> of the transmitter device <b>102</b> may be configured in a particular shape that mates with a complementary shape of the receiver device <b>104</b> (see <figref idref="DRAWINGS">FIG. 2</figref>). The illustrative second interface surface <b>114</b> may include a concave shape that follows a selected curve. The first interface surface <b>112</b> of the receiver device <b>104</b> may include a convex shape following the same or substantially similar curve as the second interface surface <b>114</b>.

0032In other embodiments, the first and second interface surfaces <b>112</b>, <b>114</b> can have any given shape and dimension. For example, the first and second interface surfaces <b>112</b>, <b>114</b> may be substantially flat. Additionally or alternatively, the transmitter and receiver devices <b>102</b>, <b>104</b> can be positioned with respect to each other using one or more alignment mechanisms. As one example, one or more magnetic devices may be included in the transmitter and/or receiver devices <b>102</b> and used to align the transmitter and receiver devices. In another example, one or more actuators in the transmitter and/or receiver devices <b>102</b> can be used to align the transmitter and receiver devices. And in yet another example, alignment features, such as protrusions and corresponding indentations in the housings of the transmitter and receiver devices, may be used to align the transmitter and receiver devices. The design or configuration of the interface surfaces, one or more alignment mechanisms, and one or more alignment features can be used individually or in various combinations thereof.

0033<figref idref="DRAWINGS">FIG. 3</figref> depicts a side cross-sectional view of the inductive energy transfer system taken along line <b>3</b>-<b>3</b> in <figref idref="DRAWINGS">FIG. 2</figref>. As discussed earlier, both the transmitter device <b>102</b> and the receiver device <b>104</b> can include electronic, mechanical, and/or structural components. For example, the receiver device <b>104</b> can include one or more processing devices, memory, a display, one or more input/output devices such as buttons, microphone, and/or speaker(s), a communication interface for wired and/or wireless communication, and a touch input device (which may or may not be incorporated into the display). The illustrated embodiment of <figref idref="DRAWINGS">FIG. 3</figref> omits the electronic, mechanical, and/or structural components for simplicity and clarity.

0034<figref idref="DRAWINGS">FIG. 3</figref> shows the example inductive energy transfer system in a mated and aligned configuration. The receiver device <b>104</b> includes one or more receiver coils having one or more windings. The receiver coil <b>300</b> may receive energy from the transmitter device <b>102</b> and may use the received energy to perform or coordinate one or more functions of the receiver device <b>104</b>, and/or to replenish the charge of a battery (not shown) within the receiver device <b>104</b>. In the illustrated embodiment, the receiver coil <b>300</b> includes sixteen windings arranged in two layers or rows. The receiver coil <b>300</b> can have a different number of windings arranged in one or more layers in other embodiments.

0035Similarly, the transmitter device <b>102</b> includes one or more transmitter coils having one or more windings. The transmitter coil <b>302</b> may transmit energy to the receiver device <b>104</b>. In the illustrated embodiment, the transmitter coil <b>302</b> includes twelve windings arranged in three layers. In other embodiments, the transmitter coil <b>300</b> can have a different number of windings arranged in one or more layers.

0036The transmitter and receiver coils can be implemented with any suitable type of inductor. Each coil can have any desired shape and dimensions. The transmitter and receiver coils can have the same number of windings or a different number of windings. Typically, the transmitter and receiver coils are surrounded by an enclosure to direct the magnetic flux in a desired direction (e.g., toward the other coil). The enclosures are omitted in <figref idref="DRAWINGS">FIG. 3</figref> for simplicity. An example enclosure is shown in <figref idref="DRAWINGS">FIG. 13</figref>.

0037Referring now to <figref idref="DRAWINGS">FIG. 4</figref>, there is shown a simplified block diagram of one example of the inductive energy transfer system <b>100</b> shown in <figref idref="DRAWINGS">FIGS. 1 and 2</figref>. The transmitter device <b>102</b> includes a power supply <b>400</b> operably connected to a DC-to-AC converter <b>402</b>. Any suitable type of a DC-to-AC converter may be used. For example, the DC-to-AC converter can be constructed as an H bridge in one embodiment. The DC-to-AC converter <b>402</b> is operatively connected to transmitter resonant circuitry <b>404</b>. The transmitter resonant circuitry <b>404</b> is operatively connected to a transmitter coil <b>406</b>. The DC-to-AC converter <b>402</b> converts a DC signal received from the power supply <b>400</b> into an AC signal, and the AC signal flows into and through the transmitter coil <b>406</b>.

0038The receiver device <b>104</b> can include a receiver coil <b>408</b> operably connected to receiver resonant circuitry <b>410</b>. The receiver resonant circuitry <b>410</b> is operatively connected to an AC-to-DC converter <b>412</b>. Any suitable type of AC-to-DC converter may be used. For example, the AC-to-DC converter can be constructed as a diode bridge in one embodiment. A load <b>414</b> is operably connected to the output of the AC-to-DC converter <b>412</b>. The load <b>414</b> is a rechargeable battery in one embodiment. A different type of load can be used in other embodiments.

0039The transmitter coil <b>406</b> and the receiver coil <b>408</b> together form a transformer <b>416</b>. The transformer <b>416</b> transfers power or energy through inductive coupling between the transmitter coil <b>406</b> and the receiver coil <b>408</b> (energy transfer represented by arrow <b>418</b>). Essentially, energy is transferred from the transmitter coil <b>406</b> to the receiver coil <b>408</b> through the creation of a varying magnetic flux by the AC signal in the transmitter coil <b>406</b> that induces a current in the receiver coil <b>408</b>. The AC signal induced in the receiver coil <b>408</b> is received by the AC-to-DC converter <b>412</b> that converts the AC signal into a DC signal. In embodiments where the load <b>414</b> is a rechargeable battery, the DC signal is used to charge the battery. Additionally or alternatively, the transferred energy can be used to transmit communication signals to or from the receiver device (communication signals represented by arrow <b>420</b>).

0040Generally, the transmitter and receiver resonant circuitry <b>404</b>, <b>410</b> may be included in the inductive charging system <b>100</b> to cancel some or all of the leakage inductance when the capacitance and inductance values are near the resonant frequency. Any suitable type of resonant circuitry can be used. In some embodiments, the transmitter resonant circuitry <b>404</b> is a resonant capacitor connected in series between the DC-to-AC converter <b>402</b> and the transmitter coil <b>406</b>, and the receiver resonant circuitry <b>410</b> is a resonant capacitor connected in series between the receiver coil <b>408</b> and the AC-to-DC converter <b>412</b>.

0041The efficiency of energy transfer in a transformer is affected by a variety of factors, including the inductance and the resistance of both the transmitter and receiver coils. Typically, the distribution or current density of an AC current in a conductive wire is largest near the surface of the wire. The current density decreases as the depth into the conductive wire increases. This phenomenon is known as the skin effect. At higher frequencies, the skin effect causes the effective resistance of the wire to increase, which results in increased resistive losses in the winding(s) of the inductor (e.g., the transmitter coil).

0042The proximity effect also adversely affects the efficiency of energy transfer in a transformer. When an AC signal flows through a conductive wire, it creates an associated alternating magnetic field around it. The alternating magnetic field induces eddy currents in an adjacent wire, altering the overall distribution of the current flowing through the two wires. The result is that the current is concentrated in the areas of the wire furthest away from the adjacent wire carrying current in the same direction. This is known as the proximity effect. The proximity effect can significantly increase the AC resistance of adjacent wires. Additionally, the proximity effect increases with frequency.

0043To reduce the losses that result from the skin effect and proximity effect in conductive wires, individual strands of wires may be twisted, woven, or braided together. One example of such a strand construction is shown in <figref idref="DRAWINGS">FIG. 5</figref>. Individual conductive strands <b>500</b> are rotated or twisted around an axis x. The axis x extends along the length of the wire and, in the illustrated embodiment, is associated with the strand in the middle position in the middle row. Each conductive strand <b>500</b> typically includes a conductive wire strand <b>502</b> having an insulation layer <b>504</b> around it. The twisted individual strands collectively form a bundle <b>506</b>.

0044In the illustrated embodiment, the bundle <b>506</b> includes seven conductive strands. Other embodiments can include a different number of conductive strands. For example, a bundle can include thirteen or nineteen strands.

0045<figref idref="DRAWINGS">FIGS. 6-8</figref> are cross-sectional views of the bundle <b>506</b> illustrating the twisting of the individual strands. Each strand is shown with a different cross-hatch pattern for identification purposes only. <figref idref="DRAWINGS">FIG. 6</figref> depicts an outer insulation <b>600</b> around the bundle of individual strands. The outer insulation <b>600</b> is optional and is therefore not shown in <figref idref="DRAWINGS">FIGS. 7 and 8</figref>.

0046Comparing <figref idref="DRAWINGS">FIG. 6</figref> with <figref idref="DRAWINGS">FIGS. 7 and 8</figref>, the individual strands are rotated or twisted in a counterclockwise direction (represented by arrow <b>700</b>) with respect to strand <b>602</b>. Other embodiments can twist the strands in a clockwise direction. Twisting the individual strands in the bundle <b>506</b> causes the individual strands around strand <b>602</b> to occupy different positions in the bundle for a given distance. If each strand has comparable impedance, current is distributed equally among every strand within the bundle, which reduces or eliminates the impact of the skin effect and the proximity effect.

0047To illustrate the different positions of the strands, the strands around strand <b>602</b> can occupy an upper left position, a middle left position, a lower left position, a lower right position, a middle left position, and an upper left position within the bundle. Looking at a particular strand <b>604</b> in the bundle, strand <b>604</b> is located in the middle left position of the bundle in <figref idref="DRAWINGS">FIG. 6</figref>. In <figref idref="DRAWINGS">FIG. 7</figref>, strand <b>604</b> is twisted to the lower right position in the bundle. And in <figref idref="DRAWINGS">FIG. 8</figref>, strand <b>604</b> is twisted to the upper right position in the bundle. Thus, all of the strands around strand <b>602</b> occupy various positions in the bundle over the length of the bundle.

0048<figref idref="DRAWINGS">FIG. 9</figref> is a perspective view of one example of a wire suitable for use in the transmitter coil <b>406</b> and/or the receiver coil <b>408</b> shown in <figref idref="DRAWINGS">FIG. 4</figref>. The wire <b>900</b> is constructed by twisting multiple bundles around an axis x. In the illustrated embodiment, four bundles <b>506</b> are twisted around the axis x. Twisting the bundles <b>506</b> causes most of the strands in each bundle to be on the outside of the wire <b>900</b> for a distance and on the inside of the wire <b>900</b> for a distance. This can further reduce the impact of the skin and proximity effects on the efficiency of energy transfer.

0049As described earlier, the wire <b>900</b> includes four bundles in the illustrated embodiment. Other embodiments can include a different number of bundles. For example, a wire can include two, three, or six bundles.

0050<figref idref="DRAWINGS">FIG. 10</figref> is a cross-sectional view of the wire <b>900</b> taken along line <b>10</b>-<b>10</b> in <figref idref="DRAWINGS">FIG. 9</figref>. An optional outer insulation layer <b>1000</b> can surround the bundles in the wire. As described earlier, the strands in each bundle rotate through various positions around a central axis over the length of the wire.

0051One advantage to the construction of the wire <b>900</b> is a higher effective cross-section usage of conductors when coiled due to compaction which creates a higher overall Q factor for the transmitter and/or receiver coils. Additionally, in some embodiments, the strands and/or bundles in the transmitter coil and/or in the receiver coil can be coated with a soft magnetic material such as iron, nickel, or cobalt to lower the AC resistance of the wire by reducing proximity effects.

0052Referring now to <figref idref="DRAWINGS">FIG. 11</figref>, there is shown a perspective view of one example of a coil suitable for use as the transmitter coil <b>406</b> and/or the receiver coil <b>408</b> shown in <figref idref="DRAWINGS">FIG. 4</figref>. The coil <b>1100</b> may be formed from a single wire <b>900</b>. The illustrative coil <b>1100</b> includes three rows or layers and four columns of the wire <b>900</b> packed into a circular structure. Thus, the coil has twelve windings. Other embodiments can include any number of layers and columns.

0053The wire <b>900</b> is interlaced within the layers such that the input end (e.g., end <b>1102</b>) and the output end (e.g., end <b>1104</b>) enter and exit the coil at substantially the same location, or substantially the same side <b>1106</b> of the coil. In the illustrated embodiment, the wire is interlaced in two layers and the input end <b>1102</b> and the output end <b>1104</b> abut one another at the location where the input end enters the coil and the output end exits the coil. Other embodiments can interlace the wire in any number of layers. Additionally, the input and output ends of the wire may enter and exit the coil at substantially the same location, or substantially the same side <b>1106</b> of the coil without abutting one another.

0054<figref idref="DRAWINGS">FIG. 12</figref> is a cross-sectional view of the coil <b>1100</b> taken along line <b>12</b>-<b>12</b> in <figref idref="DRAWINGS">FIG. 11</figref>. Each winding in the coil is numbered one through twelve and illustrates the interlaced pattern or winding configuration of the coil. The windings in layer one are linear across the columns. In other words, windings one through four are sequential across the layer. In layers two and three, the windings begin and end on layer two, move up from the second to the third layer in every other column (e.g., columns <b>1</b> and <b>3</b>), and move down from the third to the second layer in the remaining columns (e.g., columns <b>2</b> and <b>4</b>).

0055Referring now to <figref idref="DRAWINGS">FIG. 13</figref>, there is shown an expanded view of the inductive transmitter device <b>102</b> shown in <figref idref="DRAWINGS">FIGS. 1 and 2</figref>. The receiver coil <b>302</b> is included in an enclosure <b>1300</b> that surrounds three of the four sides of the coil. The enclosure shapes and directs the magnetic flux produced by the transmitter coil <b>302</b> toward the receiver coil. The shape of the transmitter coil is non-rectangular in the illustrated embodiment. As described earlier, at least a portion of the second interface surface <b>114</b> of the transmitter device <b>102</b> may have a concave shape that follows a selected curve. Thus, the transmitter coil has a trapezoid shape in the embodiment shown in <figref idref="DRAWINGS">FIG. 13</figref> so that one edge of the coil conforms to the shape of the second interface surface <b>114</b>.

0056<figref idref="DRAWINGS">FIGS. 14 and 15</figref> are expanded views of other examples of a transmitter device. In <figref idref="DRAWINGS">FIG. 14</figref>, the transmitter coil <b>1400</b> can have three layers, with one layer having 3 columns, the middle layer having four columns, and the last layer having five columns. Like the embodiment shown in <figref idref="DRAWINGS">FIG. 13</figref>, the transmitter coil <b>1400</b> can have a shape (or at least one edge of the transmitter coil can have a shape) that is complementary with the second interface surface <b>114</b>, or the transmitter coil may have a different shape.

0057In <figref idref="DRAWINGS">FIG. 15</figref>, the transmitter coil <b>1500</b> can have four layers, with each layer having 3 columns. Again, the transmitter coil <b>1500</b> can have a shape (or at least one edge of the transmitter coil can have a shape) that is complementary with the second interface surface <b>114</b>, or the transmitter coil may have a different shape.

0058The second interface surface <b>114</b> and/or the transmitter coil can have a different shape in other embodiments. For example, the second interface surface <b>114</b> can be substantially flat. In these embodiments, the shape of the transmitter coil may be rectangular. Alternatively, the transmitter coil can have a different shape, such as a helical shape. The shape of the coil can be designed to direct the magnetic flux produced by the coil and/or to reduce the distance between the transmitter and receiver coils.

0059Although the embodiments of <figref idref="DRAWINGS">FIGS. 13-15</figref> have been described with reference to a transmitter coil, the illustrate coils may be included in the receiver device. Additionally, the transmitter and/or receiver coil can have a winding configuration that positions the input end (e.g., end <b>1102</b>) and the output end (e.g., end <b>1104</b>) at substantially the same location, or substantially the same side <b>1106</b> of the coil.

0060Referring now to <figref idref="DRAWINGS">FIG. 16</figref>, there is shown a flowchart of a method for forming the coil shown in <figref idref="DRAWINGS">FIGS. 13-15</figref>. Initially, an inductor coil is formed on a mandrel by winding the wire on or around the mandrel (block <b>1600</b>). The inductor coil is formed into a first inductor coil structure. Typically, a bonding agent or adhesive is disposed on the windings to fix or secure the windings in the inductor coil structure.

0061Next, as shown in block <b>1602</b>, the bonding agent is treated to cause the bonding agent to become malleable. In some embodiments, the bonding agent can be heated to produce a pliable bonding agent. The inductor coil is then formed into a second inductor coil structure by forming the inductor coil on a mold or surface (block <b>1604</b>).

0062For example, an inductor coil can be constructed in a rectangular shape. The bonding agent in the coil can be heated and the inductor coil pressed on a curved surface to produce a trapezoid shape. At least one edge or surface of the coil, the edge in contact with the curved surface, will be formed into a shape that complements the curved surface.

0063Various embodiments have been described in detail with particular reference to certain features thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the disclosure. And even though specific embodiments have been described herein, it should be noted that the application is not limited to these embodiments. In particular, any features described with respect to one embodiment may also be used in other embodiments, where compatible. Likewise, the features of the different embodiments may be exchanged, where compatible.